With current technologies is there any cost difference or manufacturing pros/cons between using a 6mil, 8mil, 10mil via?
Assuming you also take into account proper annular ring (lets say 8mils) and aspect ratio (10:1)
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6mil drill bits cost more. Think we charge extra but don’t know how much. From a manufacturing standpoint a larger diameter is easier to work with but in this size range there isn’t much difference. We drill around 12,000,000 holes a month using these three diameters alone so it’s really a matter of what is needed.
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In the old days 5:1 depth to diameter ratio was leading edge. Many suppliers can do 8:1 these days, but beyond that you get into the realms where premiums will be added because this is leading edge technology.
There are other aspects that will influence the actual price you pay. A narrow drill bit will flex more than wider bits, so if you specified that breakout of the annular ring is not permitted, you are making it harder to drill the hole and have it come out on the other side within the acceptable zone. Remember that the glass bundles, the resin and the copper all have different hardnesses and will each influence the way the drill bit bends. Accuracy of stack alignment becomes more critical. Even the question of how much use the particular drill bit has seen will make a difference. If you specify what fibre weave you want to have, this too affects the possible accuracy of the drilling processes.
If it turns out that you do not need to use both the smallest annular ring and the smallest drill size, it is generally better to increase the size of the drill bit and keep the annular ring at its minimum as that tends to help with the tolerancing of the manufacturing processes more than if you did the opposite (i.e. use the smallest drill bit and increase the size of the annular ring).
The best advice when you’re getting very close to the limits is to talk to your supplier for the best solution, as this is usually the lowest cost and lowest risk that they will propose.
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Most manufacturers have specific minimum and maximum via sizes, and anything outside those limits will likely lead to extra costs. The same applies to trace separation—tight spacing can increase costs, especially for small production runs.
Many manufacturers offer instant quoting tools where you can upload your Gerber files and see what design constraints the system detects. If your design requires deviations from their standard settings, it usually means a price increase. The best approach is to choose your PCB manufacturer early on and understand their design limitations. Setting your DRC (Design Rule Check) based on their guidelines will help you avoid compatibility issues and costly revisions later in the process.
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When it comes to prototyping or small-scale production, smaller vias like 4mil can be more expensive and harder to source, as many manufacturers typically offer a default range of 0.2mm (8mil) to 0.3mm (12mil) for the lowest cost. Anything below 0.15mm usually incurs extra charges due to the need for specialized tooling. For affordable prototyping, Its recommended to typically set your DRC to 6mil trace/space and 0.3mm (12mil) vias, which keeps costs down and ensures compatibility with most manufacturers.
However, it’s important to remember that these constraints may change if you’re working with more advanced boards, additional layers, or higher currents, which might require different materials or thicker copper pours. Smaller vias may become necessary, but they’ll also drive up costs and complexity, so it’s worth checking with your manufacturer for their specific capabilities and cost structures before finalizing your design.
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